The present invention relates to a process for preparing esters. More particularly the invention is a method of preparing .beta.,.gamma.-unsaturated esters by contacting a .beta.,.gamma.-unsaturated carbonate with carbon monoxide in the presence of a catalyst.
It is already known to carbonylate allylic chlorides, alcohols and ethers to produce the corresponding acid derivatives. J. Tsuji et al., reported in J. Am. Chem. Soc., 86, 4350 (1964) that the carbonylation of allyl chloride in ethanol resulted in the formation of undesirable amounts of saturated and isomerized by-products. Even in the absence of a protonic reaction medium, W. T. Dent et al. reported in J. Chem. Soc., 1588 (1964) that about 10 percent yield of the isomerized 2-butenoic chloride product was obtained.
Preparation of .beta.,.gamma.-unsaturated esters by catalyzed carbonylation of unsaturated esters has been previously taught in U.S. Pat. No. 3,367,961. The products obtained were found to be usefully employed in various industrial applications.
U.S. Pat. Nos. 3,338,961 and 3,423,456 teach a process for carbonylating alkenyl halides to form the corresponding unsaturated acid halides.
U.S. Pat. No. 4,111,856 teaches certain metal chelate catalysts. The catalysts are useful among other processes for the carbonylation of olefins to acids (column 9, line 37 and Example 2).